Method of cleaning gases



Aug. 16, 1932. A. F. MESTON ET AL METHOD OF CLEANING GASES Filed March 26, 1930 Patented 16,

. UNITED STATES fPara1411" oF- Flc-E ARCHIBALD E. mEsroN, oFfEAs'r EoUN-D Dnoox, AND H Amw A. WINTEEMUTE, or rLAINErELDfNEW JEnsEY, AssIGNons 'ro RESEARCH coEroRA'rIoN, oFNEw Yonx,

N. Y., A CORPORATION OF NEW YORK nErnoD or CLEANING G'AsEs Application med'xarcn'as, 1930. sealan. 439,162.

The present invention relates to al method for eiiiciently and economicallv cleaning gases arising from metallurgical operations. Itis especially useful in cleaning gases which are produced at elevated temperatures and which can be used to best advantage while hot but which are difficult to clean unless they are cooled toa temperature approaching or below their dew point with respect to their lo moisture content.

The principal object of the present invention is to provide a method by which such hot dirt-y gases may be subjected to effective cleaning at low temperatures While conserving the sensible heat of the gases and making it available for preparing the cleaned gases for use as fuel and for other purposes.

The invention is particularly valuable in the cleaning of blast furnace gases Which-are 20 to be used as fuel in heating stoves and under boilers. These gases leave the top of the blast furnace at temperatures varying from 375 F. to 1100o F. depending upon the ore used and the practice followed in the `operation of the furnace. The gases are very dirty. They carry in suspension large amounts of finely divided ore dust, fume particles, and pieces of coke and ore that are blown through the furnace charge by the` blast. Before the gasescan be used as fuel they must be cleaned. In practically all blast furnace installations the first step in gas cleaning is the use of a dry settler. The usualform of the settler is a round vertical 'shell which utilizes to some degree the centrifugal action of the cyclone dust catcher. Coke and ore particles and considerable dust is removed in thissettler. In some installations, 50% or even more of the dirt, by Weight, is removed iin the settler.` I t provides, therefore, an important step in the cleaning of blast furnace gases, and should be retained in some form in any system directed toward the cleaning of such gases. s Because the fine particles are not removed in the dry settler, additional cleaning means are provided. A common method of cleaning the gases is to pass them through spray towers, as is well known by those versed in the art; or the gases may be cooled and humid- `iied and cleaned by electrical precipitation apparatus at low temperatures.

The invention is particularly directed to the use of a dry settler preliminarily treating the hot gases in combination With-cleaning methods and apparatus which'treatthe gases at relatively low temperatures,-for example, temperatures that are more than 200 F. below the temperature of the downcomer gases. If downcomer gases at 450 F. are wet Washed and cooled to 100 F., it is apparent that a great deal of sensible heat goes out in the cooling and Wash Water. But if the washed gases can be raised 100 to 200 F. in temperature before they reach the burners, anappreciable amount off sensible heat will be recovered. And if the hot dirty .gases can be cooled to an equal extent before they reach the Washer, the gases can be made ready for cold Wet cleaning with a small amount of cooling water.

-The invention essentially comprises bringing hot dirty gases into heat exchange relationship with theretofore cooled and cleaned gases, thereby transferring a substantial porl tion of the sensible heat of the dirty gases to the clean gases, and thereafter subjecting the cooled dirty gases to further cooling and cleaning.

A system which utilizes the savings in heat andk cooling water made possible by my invention is shown for purposes of illustration in the drawing. A combined heat exchanger and dust-catcher Which is the subject of a copending application is shown at A, connected by gas'eonducting lues to a water tower B and an electrical precipitator C. The hot, dirty, or so-called raw gas comes down from the top of the blast furnacelin pipe 10, enters and passes down space 1, turns at the bottoln ofthe space through passages 6 and chamber 7 and rises in space 2, leaves the exchanger through pipe l1, enters near the bottom of Wash tower B, leaves the Wash tower through pipe 12 and enters the electrical precipitator C. Thcgases return from electrical precipitator C by pipes 13, enter the concentric space 3 of exchanger A, pass to the bottom of space 3, enter space 4 through passages 5, and rise to the top of this space toileave theexchanger by pipe 14.

the heavy particles.

In apparatus A, the heavy dust is removed from the gases and the gases are partially cooled as they pass over surfaces which are exposed on the other side to cooler gases. When these partially cooled and partially cleaned gases enter the spray chamber B, they are further cooled, partially washed, and supersaturated with moisture. The electrical precipitator throws out the entrained moisture and suspended dust or mud in the gases which come over in pipe 12. The entrained moisture is relatively quickly precipitated by the electric field so that the material collected at the upper end of the pipes is of sludge-like consistency. This is a down-draft precipitator and so it is easy for the sludge that is thrown out near the top of the pipes' to slide downand push down all precipitated dirt with it into the sump, all precipitated dirt collecting further down the pipes which will, if not removed,

form projections on the walls of the precipitator. If these projections are permitted to form, they will increase in size, being of a relatively dry, paste-like'nature, until disruptive discharges occur,` The cleaning action of the sludge passing down the pipe prevents the formation of these deposits and thus the possibility of an arc-over is minimized. The clean, cool, saturated gases return to the heat exchanger through pipe 13 and are heated in passing through 3 and 4 where they'arc in heat exchange relationship with the hotter gases passing in 1 and 2.

This combination of apparatus uses all the equipment in a very eilicient manner. The exchanger A receives the gases at a velocity which is well adapted for the removal of The particles are removed hot and dry and can be taken from the bottom of the hopper 7 in the same manner that they are removed from any dry dust settler. This same high velocity gives as etlicient heat exchange as sturdy and easily cleaned apparatus of this general character can provide. The temperature ofthe gases is reduced in the heat exchanger to a temperature which makes humidication in tower B easily attained without excess of water. Automatic means (not shown) can be provided which' will regulate the amount of water in accordance with the temperature and humidity required in the gases. There is no need for water washing in this tower because the precipitator follows it and it can be made to cool and humidity as intended without the use of vanes or moving parts or any of the other means which are provided to make water washing more etlicient but which set up a great resistance to the flow of gases or require a great deal of power. The precipitator receives gases that are cool and of small volume, which permits this apparatus to be of minimumv size. The

gases come t0 the precipitator moist and preferably supersaturated. Such gases are usually of proper conductivity for cleaning by the well-known electrical method described in the U. S. patent to Cottrell, No. 895,729. The dust thrown out is moist and conducting, which is also a favorable condition for electrica-l precipitation. By carrying over a suflicient amount of moisture as a mist, or by spraying this needed moisture into the top header of the precipitator and precipitating this moisture with the dust, the precipitator is made self-cleaning as described in the U. S. patent to Meston, No. 1,329,844.

The temperature of the gases leaving the The gases leave saturated with moisture, and as cold gases require much less moisture for saturation than do hot gases, it is possible to reduce the moisture content of the gases by passing them through the electrical precipitator which throws out all the moisture not require for saturation (or 100% relative humidity) at the low temperature.

It will be obvious from the foregoing description that the invention is not limited to the specific embodiment shown and described for purposes of illustration, but that various modications may be made therein without departing from the scope of the invention which broadlyvcomprises a method of cleaning hot gases at low temperatures wherein the cooled gases leaving the cleaning operation are brought into heat interchange relationship with the hot dirty gases about to be subjected to the cleaning operation.

We claim:

A method of conditioning hot diity gases containing metallurgical dust in suspension which comprises cooling the hot gases by bringing them into heat interchange relationship with cool gases while subjecting the dirty gases to a dry settling o ration, humidifying the cooled gases, an passing the humidified gases downwardly through an electrostatic field at a temperature near the dew point of the gases, whereby material not hitherto removed is removed in sludgelike condition, the said cool gases being the gases which have been subjected to said cleaning operation.

In testimony whereof we aflix our signatures.

ARCHIBALD F. MESTON. HARRY A. WINTERMUTE. 

